[link to www.roytaylorministries.com]

This guy Roy figured this out years ago. He explains the levees and what it really means. In the early days of gas stations, the tanks were up on legs and gravity filled the vehicles. To prevent spills a hill or levee was mounded up around the raised tank.
So you would take your chevy to the levee for gas and the levees would be dry.

Roy is out there but his stuff in interesting to read.
Enjoy